Hormones and behaviour Flashcards
Lecture 8B (7 cards)
How do hormones influence behaviour
across a wide range of contexts including biological rhythms, eating and drinking, social behaviour, reproductive behaviour, stress
Biological rhythms
Melatonin:
1. released almost exclusively at night as inhibited by light
2. provides a signal to track daylength and season
3. controls the timing of onset of sleep
4. controls breeding condition in seasonally breeding animals
Pineal gland:
1. in birds and reptiles, can sense light directly through the skull
2. in mammals, light sensory input via retino-hypothalamic pathway
3. phasic secretion of melatonin in cyclic patterns
4. important in regulating cyclical functions
5. inhibited by light detached via the retina in the eyes
6. signal sent to suprachiasmatic nucleus in the hypothalamus, then from gere to the spinal cord, then to the cervical ganglia which inhibits pineal gland
7. suprachiasmatic nucleus is the centre of the regulation for biological rhythms in mammals
8. influences sleep onset
9. used to treat jet lag
10. also influences breeding patterns - longer autumn nights sensed, pineal gland prolongs nocturnal secretion of melatonin, hypothalamus becomes sensitive to negative feedback effects of gonadal steroids, less GnRH released, less gonadotropin released, gonad atrophy
eating and drinking
Ghrelin:
1. powerful appetite stimulant
2. circulating levels - rise prior to mealtimes and at night, drop following a meal
3. treatment with exogenous ghrelin provokes increased appetite
4. obese people have lower ghrelin before eating, following a meal their levels don’t drop
5. peptide secreted by cells in the stomach, stimulates feeding, stimulates release of growth hormone from pituitary, also secreted in the brain to control of feeding
6. other hormones and signals involved in eating behaviour - their messages are integrated in the hypothalamus
Social behaviour
Oxytocin:
1. a mammalian peptide hormone that acts on the central nervous system
2. generally associated with uterine muscle contraction at birth
3. also governs a suite of prosocial behaviours
Parental care:
1. female rats bred for high levels of maternal behaviours have more oxytocin receptors in the central nucleus of their amygdala
2. female prairie voles that show more maternal behaviour have higher oxytocin receptor density in their nucleus accumbens
3. blocking these receptors inhibits maternal behaviour
4. amygdala - small structure involved in emotions
5. nucleus accumbens - part of the reward system in the brain, involved in motivation and pleasure
Social behaviour in meerkats:
1. Madden and Clutton-Brock - 36 meerkats (28 males) injected with oxytocin vs saline control, treatments reversed 3-5 days later, recorded suite of prosocial behaviour
2. higher level of social behaviour including guarding, pup feeding, communal digging
Social behaviour in humans:
1. reciprocal relationship between hormones and behaviour
2. naturally occurring hormone-behaviour correlations do not demonstrate causal effect
Generosity:
1. Zak et al - 68 men, one shot economic game involving a voluntary donation, given oxytocin vs control nasal spray
2. donations 80% higher in oxytocin group
Reproductive behaviour
Castration in animal husbandry first observations of link between male hormones and reproductive behaviour
Endocrine and nervous systems compared
Both:
1. communication and control systems
2. take inputs and effects output
3. can be influenced by prior exposure
Nervous:
1. action potential transmitted along nerve fibre
2. some voluntary control
3. digital signal
4. responses generally short lived
5. fast response
6. diffuse effect
Endocrine:
1. slow response
2. conveyed in blood
3. analogue signal
4. chemical substance
5. targeted effect
6. response persists over time
7. no voluntary control
Neuroendocrine system
- fast initial response
- prolonged action if required
- enables regulation and control of homeostasis
- ensures that the appropriate response is given
